Fluid-mold casting process

ABSTRACT

A fluid-mold casting process produces nickel and nickel alloy ingots having improved surface and other metallurgical characteristics using a slag composition containing special amounts of alumina, lime, magnesium oxide, sodium oxide and alkaline earth metal fluoride.

United States Patent FLUID-MOLD CASTING PROCESS s can, 3 mm; Figs.

Us. Cl. 164/72, 106/3817. 148/26. 75/170. 75/128. 75/123.

Int. 01. B22d 27/911, B22c 3/00 501 FieldoiSearchW, l48/22 us.

26 US; 75/93 93 A. 96. 94. 30, 82; 164/72, 133,

References Cited UNITED STATES PATENTS Fox et a1 Fox eta lw Kennedy Dunn et a1.. Tanczyn Tanczyn Primary Examiner-J. Spencer Overholser Assistant Examiner-V. K, Rising AuorneyMaurice L. Pinel ABSTRACT: A fluid-mold casting process produces nickel and nickel alloy ingots having improved surface and other metallurgical characteristics using a slag composition containing special amounts of alumina, lime, magnesium oxide, sodiurn oxide and alkaline earth metal fluoride.

PATENTED AUG] 0 l9?! FIG FIG

FIG

INVBNTOR JAMES EARL R0 BRTS 9m ATTORNEY FLUID-MOLD CASTING PROCESS The present application is a division of may copending U.S. application Ser. No. 583,91 1 filed Oct. 3, 1966, now US. Pat. No. 3,444,010.

The present invention is directed to an improvement in the fluid-mold casting process to produce ingot castings made of nickel and nickel-containing alloys having improved surface and improved metallurgical quality and to a special casting slag composition for use in such a process.

The fluid-mold casting process has now been available to the m! for a number of years and has been employed mice-cm fully in connection with the production ol'ingot castings made of a number of different metals. In accordance with the process, a quantity of molten slag is placed at the bottom of an ingot mold and molten metal conditioned for the production of an ingot is teemed into the mold through the slag. During teeming, the slag advances upward on the surface of the metal and forms a thin coating on the ingot mold surface. The coating remains during the casting process and separates the ingot from the ingot mold. When conditions in respect of metal and slag temperature, melting point and composition of the metal and the slag are compatible, an ingot is produced having a greatly improved surface as compared to that obtained when no casting slag is employed. The initial work conducted in accordance with the fluid-mold casting process involved the use of silicate-type slags. These slags operated successfully in conjunction with the casting of metals such as mild steel and stainless steel. However, when it was attempted to use the silicatetype slags with nickel and nickelbase alloys, it was found that numerous difficulties were encountered. Thus, with many alloys, an intolerable pick up of silicon in the ingot resulting from interaction between the molten metal and molten slag was encountered, yielding ingots which did not meet chemical specifications. ln addition, defects were encountered in the surface of many ingots which have been classified as notch defect, a peripheral indentation about the ingot toward the toe portion and as shotted-surface" defect, which apparently involves emulsification of slag and metal and is usually most evident toward the top ofthe ingot. These defects required extensive and expensive overhaul of the ingots before further mill processing could be successfully undertaken. The result has been that the advantages contemplated through the use of the fluid-mold slag casting process, namely, improved ingot yield and better ingot surface, were not obtained in many instances. A further development in relation to slag chemistry involved the deletion of silica as a slag constituent and the use of a titania-calcium oxide-alumina-type slag to provide an improved fluid-mold casting composition for use with nickelcontaining alloys, particularly of the age hardening types. Further experience with this slag material has demonstrated that even further improvement was necessary. For example, it was found that in the fluid-mold casting of nickel ingots in tended for the production of wrought nickel products for electronic uses, an intolerably pickup of titanium from the slag was encountered. This resulted in ingots which were chemically out of definition and which were not acceptable. Furthermore, it was found that while in many instances highly satisfactory ingot surfaces were obtained in the production of nickel and nickel alloy ingots with the improved slag, that in other instances unsatisfactory ingot surfaces, e.g., shotted surface, were still obtained.

1 have now discovered an improved casting slag composition and process for fluid-mold casting of nickel, nickel-base and nickel-containing alloys which provides improved ingot surfaces and greater recovery of metal from the ingot into hot rolled products.

It is an object of the present invention to provide an improved fluid-mold casting slag particularly useful for the production of ingots made of nickel and nickel-containing alloys.

Another object of the invention is to provide a fluid-mold casting process applicable to nickel and nickel-containing alloys which provides improved ingot surface and improved metal yield upon hot rolling of the ingots, as well as improved metallurgical quality.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a reproduction of a photograph depicting the surface ofa 20 inch square by inch long nickel ingot produced in accordance with the concepts of the present invention;

HO. 2 is a reproduction of a photograph depicting the surface ofa 20 inch square by 90 inch long nickel-chromium-iron alloy ingot produced in accordance with the invention; and

FIG. 3 is a reproduction ofa photograph of a hot rolled billet produced from an age hardenable nickel-chromium alloy ingot cast in accordance with the invention which was hot rolled without any surface overhauling.

Generally speaking, the present invention is directed to a casting slag composition consisting essentially of, by weight, about 20 percent to about 40 percent alumina, about 25 percent to about 50 percent calcium oxide, with the alumina content not exceeding the calcium oxide content by more than 5 weight percent, about 5 percent to about 20 percent magnesium oxide, about 3 percent to about 10 percent sodium oxide, and about 10 percent to about 30 percent of an alkaline earth fluoride ingredient from the group consisting of cryolite (N33AIF6)! potassium aluminum florride lgAlF and floursnar (C fe. dyanta sq ly e s st s sl qmgq iti n contains about 35 percent to about 50 percent calcium oxide, about 25 percent to about 40 percent alumina, about 5 percent to about 15 percent magnesia, about 10 percent to about 30 percent of an alkaline earth fluoride, from the group consisting of cryolite, potassium aluminum fluoride, calcium fluoride and about 3 percent to about 10 percent sodium oxide. A preferred slag composition contains about 35 percent to about 40 percent calcium oxide, about 25 percent to about 40 percent alumina, about 5 percent to about 8 percent magnesia, about l0 percent to about 20 percent cryolite, about 5 percent to about It) percent fluorspar and about 3 percent to about 6 percent sodium oxide. The slags produced in accordance with the invention have a flow point on heating in the temperature range of about 2,30() F. to about 2,450 F. The special slag compositions are essentially devoid of silica and titania, although, in some instances, for example, those in which minor pickup ofsilicon is permissible up to about 3 percent silica may be present. Titania should not exceed about 0.5 percent, by weight, e.g., 0.1 percent or 0.2 percent. Metal oxides such as manganese oxide, chromium oxide, nickel oxide and copper oxide are preferably absent but may be in some cases present in amounts up to about 1 percent each. lmpurities harmful to nickel and nickel alloys, including arsenic, lead, tin, zinc, sulfur, etc., should be absent from the slag. For purposes of controlling the fiow point on heating the slag to be in the advantageous neighborhood of 2,300 to about 2,450 F. in the case of nickel and nickel-containing alloys, including nickel-chromium, nickel-chromium-iron, nickel-copper alloys, cupronickel alloys, etc., the ingredients for forming the slag are carefully proportioned. The bulk of the slag composition comprises calcium oxide and alumina with the alumina being present in amounts not exceeding the calcium oxide by more than 5 weight percent. Magnesia and sodium oxide in the controlled amounts specified hereinbefore assist in controlling the melting point. Magnesia is employed in amounts not exceeding 20 percent and preferably not exceeding about l5 percent since greater amounts undesirably raise the slag melting point. The fluoride ingredients, namely, cryolite, potassium aluminum fluoride and fluorspar, are employed in the amounts described for purposes of further controlling fluidity and melting point of the slag. ln compounding the slag, it is important that the dry ingredients be thoroughly blended prior to melting since it is otherwise found impractical to secure a uniform slag composition in the melting procedure. Melting advantageously is conducted in a submerged electrode furnace. A number of satisfactory slag compositions are set forth in the following table I:

TABLE I Flow point on C110, Alan. .\Ig(,), (til-g, NaIAII'H, KzAl Ft. N820. heating Slag No. percent percent percent percent percent percent percent 1 a: a7 a s 10 2, 440 .3 35 as s s 14 5 2,400 3 43 27 5 10 5 2,320 4 3T 3T 6 I5 5 2,440 5 35 35 10 5 2,380

The special casting slag composition is particularly ad- 10 remaining ingot molds were then filled in the same manner.

vantageous for the production of ingots in commercial wrought nickel containing 99 percent and more of nickel, nickel-copper alloys containing 50 percent or more of nickel, cupronickel alloys containing nickel in amounts as low as about 29 percent and the balance essentially copper, and nickel-chromiurn-iron alloys containing percent or more of nickel, up to 50 percent of iron and up to 30 percent of chromium. The alloys may also contain other usual alloying ingredients such as up to about l0 percent molybdenum, up to about 10 percent columbium, up to about 30 percent cobalt, up to about 5 percent tungsten, up to about 5 percent manganese, up to about 3 percent silicon, up to about 0.5 percent carbon. up to about 2 percent vanadium. up to about 6 percent aluminum, up to about 6 percent titanium, up to about 0.2 percent zirconium, up to about 0.5 percent magnesium, etc. Stainless steels containing as little as 7 percent nickel and up to 75 percent iron may also be treated in accordance with the invention.

Compositions of nickel-containing alloys which may be satisfactorily fluid-mold cast in accordance with the invention are set forth in the following table II:

Metal from the ingots met the rigid chemical specification for this grade of material. The resulting ingots were inspected and found to have an excellent surface which permitted them to be hot rolled without any surface overhauling. The surface of one of the ingots in depicted in the accompanying FIG. 1.

It was found that the use of the special casting slag in accordance with the foregoing example eliminated the ingot cracking problem which has been encountered during solidification of nickel ingots heretofore. Such cracks rupture during hot working with major losses of metal. Elimination of the ingot cracking and the ingot overhauling in this electronic grade of nickel provides a yield increase at the hot rolling stage on the order of 6 percent to 8 percent by weight. The

' fluid-mold cast material was not only hot rolled from the ingot stage without overhaul of the ingot surface but it was found that when the material was worked down into strip form blistering was 70 percent less than on strip produced from nonflux cast ingots.

EXAMPLE II An ingot of a nickeI-chromium-iron alloy containing about TABLE II Alloy Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent N0. N1 Mn Fe Cu Cr AI i other CoIumbium.

I Molybdenum.

In order to give those skilled in the art a better understanding of the invention, the following illustrative examples are given:

EXAMPLE] A melt weighing about 9,880 pounds made of a commercially pure nickel alloy containing about 99.5 percent nickel, about 0.09 percent carbon, not more than about 0.3 percent manganese, not more than about 0.1 percent iron. not more than about 0.1 percent silicon, not more than about 0.1 percent copper, and not more than about 0.003 percent titanium was prepared for casting in an induction furnace. A casting slag melt made from a charge of blended dry ingredients containing about 37 percent calcium oxide, about 37 percent alumina, about 6 percent magnesia, about 5 percent fluorspar about 10 percent cryolite and about 5 percent sodium oxide added as sodium carbonate was prepared in a submerged electrode furnace and was heated to about 3,l00 F. 20 inch by 20 inch square ingot molds were set up on copper stools. About 250 pounds of the molten casting slag was poured into the bottom of the first ingot mold. This was sufficient to extend upwards within the ingot mold and cover about 3 inches vertically at the bottom of the mold. Nickel from the induction furnace heat was teemed from a bottom pour ladle at a temperature of about 2,870 F. into the ingot mold at a steady rate through the slag pool to completely fill the ingot with metal and flush the excess casting slag from the top of the mold. The

3.2 percent nickel, about 0.04 percent carbon, about 0.75 percent manganese, about 0.35 percentsilicon, about 0.3 percent copper, about 20.5 percent chromium, and the balance essentially iron, was produced by the fluid-mold process employing a fluid-mold casting slag having the composition set forth in example I. When the ingot was stripped from the mold, it was found to have a high quality surface free from the shotting defeet. The appearance of the ingot is depicted in the accompanying FIG. 2. The highly satisfactory result achieved with this material contrasts with the results obtained in fluid-mold casting the alloy using both the silicate-type slag and the titania-Iime-alumina slag of the prior art. Each of the prior art casting slags resulted in a shotted surface with this alloy. Thus, with the silicate-type slag about 75 percent of ingots produced from this alloy required milling and about 60 percent ofingots produced in this alloy using the titania-Iime-alumina slag required milling. However, the ingots produced with the new fluid-mold casting composition described herein could be hot rolled without ingot overhauling thereby enabling a yield increase at the hot rolled stage on the order of 3 percent to 5 percent by weight.

EXAMPLE III Ingots made of an age hardenable nickel-chromium alloy containing about 7 percent iron, about 16 percent chromium, about 3 percent titanium, about 0.04 percent carbon, about 0.15 percent silicon, and the balance essentially nickel, were produced by the fluid-mold casting process employing a slag having the composition set forth in example i. The ingots were l8 inches square and 48 inches long. ingots stripped from the mold demonstrated an excellent surface which permitted hot rolling to bloom without ingot overhaul. The surface of a hot rolled shape having a 10 inch by inch section produced from the IS inch square ingot of this alloy without ingot overhaul is depicted in the accompanying FIG. 3. It was found that with this particular alloy the prior fluid-mold casting slags did not produce results any better than those achieved with no slag at all. The ability to produce the high quality ingot surface on this alloy using the special fluid-mold casting slag of the present invention enables a yield increase at the hot rolled stage on the order of about 10 percent by weight as compared to prior practice.

The special fluid-mold casting slag compositions provided I in accordance with the invention must be carefully controlled to secure the desired results. In particular, the alumina con tent should not exceed the lime content by more than 5 weight percent while maintaining other slag ingredients in the ranges set forth hereinbefore or it becomes impractical to obtain the required melting point even with the use of fluoride ingredients. For example. a slag containing 5 moles of CaO and 3 moles of AI,O with no other ingredients representing a weight content of 52.5 percent Al,0,, has a flow point on heating which is far in excess of 2,450 F. and remains too sluggish and refractory to produce good nickel alloy ingot surfaces in slag casting even when diluted with a fluoride ingredient such as fluorspar.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be restored to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

lclaimv l. in the method for fluid-mold casting ingots made of nickel and nickeLcontaining alloys containing at least about 7 percent nickel wherein a quantity of molten casting slag is preplaced in the bottom of an ingot mold and the ingot-forming molten metal is poured through the slag pool to cause the slag to float toward the top of the ingot mold in advance of the rising molten metal surface during the teeming of the ingot whereby the slag solidifies continuously against the ingot mold surface and forms a shell between the outer face of the ingot and the inner face of the ingot mold. the improvement for producing an ingot face of high quality which comprises employing as a casting slag a composition consisting essentially of by weight, about 20 percent to about 40 percent of alumina, about 25 percent to about 50 percent of calcium oxide, with the alumina content not exceeding the calcium oxide content by more than 5 weight percent, about 5 percent to about 20 percent magnesium oxide, about 3 percent to about 10 percent sodium oxide, and about 10 percent to about 30 percent of a fluoride ingredient.

2. A method in accordance with claim 1 wherein the casting slag contains about 35 percent to about 50 percent calcium oxide, about 25 percent to about 40 percent alumina, about 5 percent to about 15 percent magnesia, and about l0 percent to about 30 percent of an alkaline earth fluoride.

3. A method in accordance with claim 1 wherein the casting slag contains about 35 percent to about 40 percent calcium oxide, about 25 percent to about 40 percent alumina, about 5 percent to about 8 percent magnesia, about 3 percent to about 6 percent sodium oxide, about 10 percent to about 20 percent cryolite and about 5 percent to about 10 percent fluorspar.

4. A method in accordance with claim 1 wherein the casting slag contains about 35 percent to about 43 percent calcium oxide, about 27 percent to about 37 percent alumina, about 6 percent to about 10 percent magnesia, about 5 percent sodium oxide and about 15 percent to about 19 percent of a flouride ingredient from the group consisting of fluors par, cryolite and potassium aluminum fluoride.

5. A method in accordance with claim 1 wherein the casting slag contains about 37 percent calcium oxide, about 37 pe'rcent alumina, about 6 percent magnesia, about 5 percent sodium oxide about 5 percent calcium fluoride and about [0 percent cryolite.

UNITED STATES PATENT OFFICE (569) CERTIFICATE OF CORRECTION Patent 3r598.l70 Dated Angnqim 1Q' 7l Inventor(s) JAMES E. ROBERTS It is certified that: error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 3, for "may" read my--.

Line 49, between "alumina" and "type" delete the hyphen Line 57, for "intolerably" read --intolerable-. 11116 26 r for "florride" read --fluoride--. Col. 2, line 26, for "K AlF read --(K AlF Col. 4 line 48, for "3.2" read ---32---.

C01. 5, line 23, after "gradients" insert a period Signed and sealed this 16th day of May 1972.

(SEAL) At best:

EDNAhD ILFLE TC HER J H ROBERT GO TTSCHQLK Atng Officer Commissioner of Pa be n'us 

2. A method in accordance with claim 1 wherein the casting slag contains about 35 percent to about 50 percent calcium oxide, about 25 percent to about 40 percent alumina, about 5 percent to about 15 percent magnesia, and about 10 percent to about 30 percent of an alkaline earth fluoride.
 3. A method in accordance with claim 1 wherein the casting slag contains about 35 percent to about 40 percent calcium oxide, about 25 percent to about 40 percent alumina, about 5 percent to about 8 percent magnesia, about 3 percent to about 6 percent sodium oxide, about 10 percent to about 20 percent cryolite and about 5 percent to about 10 percent fluorspar.
 4. A method in accordance with claim 1 wherein the casting slag contains about 35 percent to about 43 percent calcium oxide, about 27 percent to about 37 percent alumina, about 6 percent to about 10 percent magnesia, about 5 percent sodium oxide and about 15 percent to about 19 percent of a fluoride ingredient from the group consisting of fluorspar, cryolite and potassium aluminum fluoride.
 5. A method in accordance with claim 1 wherein the casting slag contains about 37 percent calcium oxide, about 37 percent alumina, about 6 percent magnesia, about 5 percent sodium oxide about 5 percent calcium fluoride and about 10 percent cryolite. 